The long-term goal of this project is to determine how the cell wall-less mycoplasmas interact with their eukaryotic hosts. Current emphasis involves the elucidation of the roles of viruses and plasmids in the determination of surface characteristics of mycoplasmal cells. Extra-chromosomal DNA's have been identified, using agarose gel electrophoresis, in several mycoplasma, acholeplasma and spiroplasma strains. Assignment of specific plasmids as intra-cellular forms of previously described viruses is underway. Several Acholeplasma laidlawii strains can be stimulated to release viruses after treatment with mitomycin C. Using spiroplasma strains, similar virus induction has been unsuccessful. Spiroplasma cells, when infected with group 1 virus, can survive suboptimal conditions better than uninfected spiroplasmas. Similarly infected A. laidlawii strains show no selective advantage. Whole cell polypeptide profiles, using polyacrylamide gel electrophoresis, reveal few if any differences between uninfected and chronically infected mycoplasmas. Continued work using the enveloped plasma-viruses is being carried out in an attempt to learn more about cell membrane involvement in the virus infection cycle.